1. Field of the Invention
The present invention relates to an ultrasonic diagnostic apparatus and a catheter tip part detection method, and more particularly, to an ultrasonic diagnostic apparatus and a catheter tip part detection method which make it possible to detect a position coordinate of a tip part of a catheter, an ultrasonic probe having a thin diameter or the like inserted into a body of an object.
2. Description of the Related Art
The ultrasonic diagnostic apparatus performs ultrasonic transmission/reception in a plurality of directions in a patient body using an ultrasonic probe with a plurality of transducers arranged therein, and displays, on a monitor, ultrasonic image data generated based on reflected waves obtained during the ultrasonic transmission/reception. Because the ultrasonic diagnostic apparatus allows two-dimensional images or three-dimensional images in the body to be observed in real time by a simple operation of bringing an ultrasonic probe into contact with the body surface, it is extensively used for shape diagnosis or functional diagnosis of various organs.
Performing a treatment such as transcatheter arterial embolization (TAE), percutaneous transluminal coronary angioplasty (PTCA), percutaneous transluminal coronary recanalization (PTCR) or radiofrequency ablation (RFA), or various diagnoses, while ascertaining the position of the tip part of a catheter or a small-diameter ultrasonic probe inserted into a blood vessel or a digestive tract, or a puncture needle inserted into body tissues (hereinafter these are collectively referred to as a “catheter”), under the observation of real-time displayed ultrasonic image data, allows the accuracy and safety in an examination or treatment to be drastically improved. In addition, the diagnosis/treating method using ultrasonic image data has an advantage in being free of X-ray exposure compared with that using X-ray image data which has hitherto been executed for the same purpose.
However, when attempting to concurrently acquire information on the body tissues and information on the catheter tip part using the ultrasonic probe arranged on the body surface of an object, it has been difficult to make a constant observation of the catheter tip part, on the ultrasonic image data, because ultrasonic waves radiated from the transducers in the ultrasonic probe make specular reflections (mirror reflections) on the smooth surface of the catheter.
Specifically, since a diameter of a general catheter is about 2-3 mm, it is impossible to observe a general catheter on an ultrasonic image with enough accuracy though the catheter can be observed to a certain extent. Particularly, when an RITA (radio frequency interstitial tissue ablation) needle is attached with a catheter for RFA, it is impossible to observe the RITA needle on an ultrasonic image absolutely since the diameter of the RITA needle is not over 1 mm.
In order to solve such a problem, a method has been proposed wherein a minute transducer for receiving ultrasonic waves is mounted on the catheter tip part, and ultrasonic waves radiated from transducers in the ultrasonic probe arranged on the body surface of the object are received using the transducer at the catheter tip part to thereby detect the tip position thereof (see, for example, Japanese Patent Application (Laid-Open) No. 4-129543).
Another method has also been proposed wherein ultrasonic waves radiated from the transducer mounted on the catheter tip part are received by each of three discrete transducers in the ultrasonic probe arranged on the body surface of the object, and the tip position of the catheter is detected based on delayed times between the three obtained reception signals (see, for example, Japanese Patent Application (Laid-Open) No. 2002-315754). According to this method, a display of position information on the catheter tip part can be superimposed on a display of three-dimensional image data on blood vessels or the like acquired by the ultrasonic probe, or a display of endoscopic image data as seen from the viewpoint of the catheter tip part (so-called fly-through image data) can be achieved.
By the above-described methods which are described on Japanese Patent Application (Laid-Open) No. 4-129543 and Japanese Patent Application (Laid-Open) No. 2002-315754, the catheter tip part can be detected independent of the material and the shape of the catheter, and the incident angle of ultrasonic waves radiated from the transducers in the ultrasonic probe.
However, in these methods, broadband ultrasonic pulses radiated from the transducer mounted on the catheter tip part or the transducers in the ultrasonic probe arranged on the body surface are received by the transducers in the ultrasonic probe or the transducer mounted on the catheter tip part, and arrival times (delayed times) of the obtained pulses are measured to thereby detect the position of the catheter tip part. Therefore, if a non-negligible ultrasonic attenuation occurs in the body tissues intervening between the ultrasonic probe and the catheter, the reception sensitivity of ultrasonic pulses in the transducers in the ultrasonic probe or the transducer at the catheter tip part is deteriorated, and also, in the above-described ultrasonic pulses having a broadband frequency spectrum, the higher the frequency of a pulse component, the larger becomes the attenuation that the component undergoes. As a result, the waveforms of the ultrasonic pulses are significantly deformed, thereby making it difficult to accurately measure the arrival times of the ultrasonic pulses.
Furthermore, according to the above-described methods which are described on Japanese Patent Application (Laid-Open) No. 4-129543 and Japanese Patent Application (Laid-Open) No. 2002-315754, when sound speeds of ultrasonic waves in body tissues are uneven, it is undesirably difficult to accurately detect the position of the catheter tip part even if the above-described arrival times are accurately measured, because the arrival times of ultrasonic pulses depend on positions of transducers in the ultrasonic probe or body tissues.